Arrangement and method for removing alkali- or alkaline earth-metals from a vacuum coating chamber

ABSTRACT

The invention relates to a cleaning method in which from a vacuum coating chamber ( 3 ) of a coating installation ( 1 ) for the coating of substrates ( 2 ) with alkali- or alkaline earth-metals, residues of alkali- or alkaline earth-metals are removed. For this purpose into the chamber ( 3 ) a gas from the group of N 2 , O 2  or air is introduced, which reacts with the alkali- or alkaline earth-metals to form the corresponding solid compounds. Water can additionally be introduced into the vacuum coating chamber ( 3 ). 
     After the alkali- or alkaline earth-metals have reacted with the gas, the corresponding solid compound is removed from the vacuum coating chamber.

FIELD OF THE INVENTION

The invention relates to an arrangement and a method for removing metalsfrom a vacuum coating chamber.

BACKGROUND OF THE INVENTION

Modern lithium batteries are, as a rule, produced in a vacuum chamber,wherein a substrate is provided with a lithium layer. The lithium layeris formed, for example, through the deposition on the substrate oflithium in the vapor state. Since lithium is highly reactive, contact bythe operating personnel after opening the vacuum chamber must beavoided. Even if the excess lithium has been pumped out of the vacuumchamber, it is still possible for lithium particles deposited on theinner wall of the vacuum chamber or on facings and/or maskings to harmthe operating personnel.

Methods for the production of lithium batteries are already known inwhich lithium is converted in a vacuum chamber into vapor, which issubsequently deposited on a substrate (JP 59-060866, JP 2003-007290, JP2003-234100, JP 2007-207663). Nothing is found in these publicationsregarding the cleaning of the vacuum chamber.

It is further known to eliminate undesirable depositions on the insideof a coating installation by means of a cleaning gas (JP 2003-229365).However, lithium or alkali metals are herein not listed.

Furthermore, cleaning a process chamber by means of a gas containing O₂is known (US 2007/0163617 A1). Herein the cleaning is carried out atincreased temperature and under vacuum. The gas preferably also containsH radicals, since the cleaning process can also be carried out by meansof a plasma. However, the walls of the process chamber are cleaned oftungsten and not of lithium or another aggressive material.

A further method for cleaning coating chambers is disclosed in DE 103 38275 A1. In this method the process chamber is flushed with a conditionedpurge gas before a coating process. The purge gas is preferablycomprised of O₂ and N₂ with a humidity value of maximally 30%. Thecoating chamber is cleaned before the coating process and the coatingmaterial is not lithium.

US 2002/0185067 A1 discloses a device and a method for the in situcleaning of a throttle valve in a CVD system. Here a cleaning gas isintroduced which can comprise F₂, C₂F₆, O₂ or NF₃. Lithium is notdiscussed.

A cleaning process for a coating chamber is furthermore known in whichinter alia N₂ and O₂ are employed as cleaning gases (EP 1 612 857 A1).These gases are converted to plasma and subsequently serve for cleaningthe inner wall of a CVD chamber. High frequency is utilized for thegeneration of the plasma. However, not Li, but rather Si₃N₄ or SiO₂ areremoved.

EP 0 441 368 A discloses a device and a method for eliminating excessmaterial from a PVD chamber. During a cleaning cycle a vacuum isgenerated in the PVD chamber and a gas mixture with reactive gas isintroduced into the PVD chamber. The reactive gas is herein activatedthrough plasma discharge. The objects of the cleaning are alsoscreenings. The eliminated material is Ti, W or Al, not however Li.

The invention addresses the problem of cleaning such parts of a vacuumcoating chamber which during the production of thin-film batteries areunintentionally coated, for example maskings, metal lining sheets andthe like.

SUMMARY OF THE INVENTION

The advantage attained with the invention comprises in particular thatunintentionally coated parts are cleaned in simple manner and the cycletimes or service times are shortened. Since the cleaning can also becarried out cyclically, it is possible to operate a coating installationwithout interruption.

The invention consequently relates to a cleaning method in which from avacuum coating chamber of a coating installation for the coating ofsubstrates with alkali- or alkaline earth-metals, residues of alkali oralkaline earth-metals are removed. For this purpose into the chamber agas from the group of N₂, O₂ or air is introduced which reacts with thealkali- or alkaline earth-metals to form the corresponding solidcompounds. Water can still also be additionally introduced into thevacuum coating chamber.

After the alkali- or alkaline earth-metals have reacted with the gas,the corresponding solid compound is removed from the vacuum coatingchamber.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment example of the invention is shown in the drawing and willbe described in further detail in the following. In the drawing depict:

FIG. 1 a vacuum chamber for coating a substrate by means of a vaporizedmaterial.

DETAILED DESCRIPTION

A coating installation 1, in which a substrate 2 can be coated, is shownin FIG. 1 in sectional view. This coating installation 1 includes avacuum coating chamber 3, of which two side-walls 4, 5 are evident.Masking 6 is disposed between the substrate 2 and a vapor feed system 7,which comprises a vaporizer crucible 8, a valve 9 and a vapor inlet 10to 13. The end of the vapor inlet is formed by a linear distributor 14implemented as a vertically oriented tube with linearly disposedopenings. These openings are located opposite the masking 6. By 15, 16are denoted covers in the vacuum chamber 3.

In the vaporizer crucible 8 is melted, for example, lithium for theproduction of thin-film lithium batteries and vaporized. Instead oflithium, another reactive metal from the group of alkali- and alkalineearth-metals, for example cesium, could also be utilized.

The vaporized material arrives via the vapor inlet 10 to 13 at thedistributor 14 and from here, via the masking 6, which does not need tobe provided in every case, at the substrate 2. In addition, thevaporized material also reaches the covers 15, 16 and other parts whichit is not intended to reach.

When the coating of substrate 2 is completed, the unintentionally coatedparts must be freed of the coating in order for the operating personnelnot to be harmed by the reactive lithium when opening the vacuum chamber3 and removing the coated substrate 2.

However, in order for a person not to come into contact with the lithiumor other alkaline earth- or alkali-metals, these metals must be removedfrom the installation. The removal of these reactive metals from theinstallation takes place after the coating process has been terminatedand the substrates have been transferred from the coating installation 1via a vacuum lock, not shown in FIG. 1. After the substrates have beenremoved from the coating installation 1, one or several gases areintroduced into the vacuum chamber 3 before the opening the vacuumchamber 3.

For this purpose, outside of vacuum chamber 3 several gas containers 20,21, 22 are provided which contain the gases N₂, O₂ or air. Activation ofthe gases is not absolutely required. These gas tanks 20, 21, 22 areconnected via supply pipes 23, 24, 25 and valves 26, 27, 28 with thevacuum chamber 3. If N₂ is introduced into the vacuum chamber 3, the N₂molecules combine with lithium according to the equation 6 Li+N₂→2 Li₃N.This end product is a solid which falls from the vertical surfaces tothe bottom of the vacuum chamber 3 or adheres at the site of thereaction.

If O₂ is introduced into the vacuum chamber 3, based on the expression 4Li+O₂ the colorless powdery solid compound Li₂O is formed, which is alsonontoxic and falls from vertical parts.

It is understood that instead of pure oxygen, air can also be introducedinto the vacuum chamber 3. This air can herein be enriched with O₂.Since air contains both nitrogen as well as also oxygen, lithiumconsequently reacts with the nitrogen as well as also with the oxygen.It is here advantageous if the air has a certain humidity. To this endthe air can additionally be enriched with water. If there is also watercontained in the air, the following reaction takes place:

Li+H₂O→LiOH+½H₂.

When air and water are introduced, in addition to Li₃N and Li₂O, LiOHand Li₂CO₃ are also formed.

For instance, Li₂CO₃ is formed through the following reaction: 2LiOH+CO₂→Li₂CO₃+H₂O.

At high temperatures Li₂CO₃ breaks down again into Li₂O and CO₂. Thesame applies also to LiOH which breaks down into Li₂O and H₂O. Thelithium compounds must in every case be nontoxic and remain stable inair.

Since the reactions of H₂O, O₂ and N₂ are exothermic, it is advantageousto cool the vacuum chamber 3. This can be carried out by means of acooling system, not depicted in FIG. 1.

In principle, the metal Li, or also the other alkali- and alkalineearth-metals, can be made to react with other substances, such as, forexample, with halogens or hydrogen compounds of these halogens.

However, since these halogens or halogen compounds are highly reactiveand can also chemically attack the chamber, it is necessary whenemploying these compounds to build the chamber of a material that ischemically inert relative to these compounds.

Although activation of the gases is not absolutely required, it isnevertheless advantageous to carry out the reaction at increasedtemperatures. A temperature in the range from 30° C. up to 200° C. canbe selected, at which the reaction is started. It is obvious that athigher temperatures the reaction proceeds faster. It is of advantage ifthe reaction takes place at a pressure of up to 100 mbar. The choice oftemperature as well as of pressure depends substantially on the designof the vacuum chamber 3. If only pure oxygen is utilized as the gas, thetemperature can be, for example, 80° C. and the pressure of the oxygen100 mbar. This ensures optimal reaction conditions.

It is advantageous if during the cleaning process the reaction ismonitored by means of a gas sensor 32. A gas sensor 32 to be consideredis, for example, a mass spectrometer, a lambda probe or an IR or NIRspectrometer. Via these measuring devices the gas composition can bedetermined during the process. If a lambda probe is employed, oxygen ispreferably added to the gas or gas mixture. In this case the oxygencontent can be determined during the process. As long as there is stilllithium in the chamber and reacts with the gases, the concentration ofthe reactive gases is below the concentration of the gases before theirintroduction into the vacuum chamber 3 vitiated with lithium. As soon asthe lithium has reacted with the gases, the concentration of the gasesreaches the starting value again. This indicates that the reactionprocess has been completed. The gas composition, which had beendetermined by means of the gas sensor 32, is supplied to an evaluationinstrument 33. When the process is completed, by means of a pump 30 andan extraction fitting 31 the powder on the bottom of the vacuum chamber3 can be suctioned out. It is also possible to vent the vacuum chamber 3and subsequently to remove the powder by means of a dust extractor. Itis herein advantageous to remove the lithium salt adhering on the wallsof the vacuum chamber 3 by means of ultrasound such that it falls to thebottom. This facilitates the cleaning work considerably. By settingparameters such as, for example, pressure, temperature or the moisturecontent in the form of water in the gas or the gas mixture, the reactionwith the lithium can be accelerated. In order to enrich gases withmoisture, water is introduced into the vacuum chamber 3 via a feed pipe35.

Whether the lithium salts remain adhered to the surface after thecleaning process or spall off and consequently fall to the bottom of thevacuum chamber 3 depends substantially on the layer thicknesses of theformed lithium salts. If the lithium layers formed in the coatingreaction are very thin, salts with a very small grain diameter areformed in the cleaning process. Such lithium layers remain preferablywell adhered on the walls of the vacuum chamber 3. If during the coatingprocess thick lithium layers have been formed on the walls of the vacuumchamber, layers are formed in the cleaning reaction with the gases,which layers are under mechanical stress, which can lead to the spallingof the coating. For this reason it can be advantageous to remove thesalt residues still adhering on the walls of the vacuum chamber 3 bymeans of ultrasound.

1. Arrangement for removing alkali- or alkaline earth-metals from avacuum coating chamber (3) of a coating installation (1) with at leastone gas tank (20-22) connected via a supply pipe (23-25) with the vacuumcoating chamber (3), which gas tank contains a gas from the group N₂, O₂or air.
 2. Arrangement as claimed in claim 1, characterized in thatbetween the at least one gas tank (20-22) and the vacuum coating chamber(3) a valve (26-28) is provided.
 3. Arrangement as claimed in claim 1,characterized in that the vacuum coating chamber (3) includes a feedpipe (35) for H₂O, via which H₂O can be introduced into the vacuumcoating chamber (3).
 4. Arrangement as claimed in claim 1, characterizedin that the vacuum coating chamber (3) includes means with which thevacuum coating chamber (3) can be exposed to ultrasound.
 5. Arrangementas claimed in claim 1, characterized in that the vacuum coating chamber(3) includes at least one gas sensor (32).
 6. Arrangement as claimed inclaim 5, characterized in that the gas sensor (32) is a massspectrometer.
 7. Arrangement as claimed in claim 5, characterized inthat the gas sensor (32) is a lambda probe.
 8. Arrangement as claimed inclaim 1, characterized in that the vacuum coating chamber (3) includesat the bottom an extraction fitting (31) which is connected to a pump(30).
 9. Arrangement as claimed in claim 5, characterized in that thegas sensor (32) is an IR or NIR spectroscope.
 10. Arrangement as claimedin claim 1, characterized in that the metal is lithium.
 11. Method forremoving alkali- or alkaline earth-metals from a vacuum coating chamber(3) of a coating installation (1), characterized by the following steps:a) the vacuum coating chamber (3) is set under vacuum after the coatingprocess has been completed, b) a gas from the group of N₂, O₂ or air isintroduced into the vacuum coating chamber (3) such that the gas reactswith the alkali- or alkaline earth-metals in the vacuum coating chamber(3) and forms a solid compound, c) the solid compound is removed fromthe vacuum coating chamber (3).
 12. Method as claimed in claim 11,characterized in that the metal is lithium.
 13. Method as claimed inclaim 11, characterized in that H₂O is additionally introduced into thevacuum coating chamber (3).
 14. Method as claimed in claim 11,characterized in that the air is enriched with O₂.
 15. Method as claimedin claim 11, characterized in that the gas content during the reactionis determined by means of a gas sensor (32).
 16. Method as claimed inclaim 15, characterized in that the gas content is determined by meansof a mass spectrometer.
 17. Method as claimed in claim 15, characterizedin that the oxygen content is determined by means of a lambda probe. 18.Method as claimed in claim 11, characterized in that at the beginning ofthe process a temperature of 30° C. up to 200° C. is set.
 19. Method asclaimed in claim 18, characterized in that the temperature is 80° C. 20.Method as claimed in claim 11, characterized in that a pressure of 100mbar is set.
 21. Method as claimed in claim 11, characterized in thatthe solid compound is removed from the vacuum coating chamber (3) bymeans of an extraction fitting (31) connected to a pump (30).
 22. Methodas claimed in claim 11, characterized in that the solid compound isremoved from the vacuum coating chamber (3) by means of a dustextractor.
 23. Method as claimed in claim 21, characterized in that thesolid compound formed is detached by means of ultrasound from the wallsof the vacuum coating chamber (3) before being removed from the vacuumcoating chamber (3).
 24. Method as claimed in claim 22, characterized inthat the solid compound formed is detached by means of ultrasound fromthe walls of the vacuum coating chamber (3) before being removed fromthe vacuum coating chamber (3).
 25. Method as claimed in claim 15,characterized in that the gas content is determined by means of an IR orNIR spectroscope.